1. Field of the Invention
This invention relates to composite elastomeric springs and, more particularly, to hollow composite elastomeric springs capable of providing a variable rate spring load versus deflection curve under certain load conditions.
2. Description of the Related Art
There are many applications in which it is desirable to obtain a variable rate load versus deflection curve at or above certain load levels or deflections. Elastomeric springs often are selected for such applications, because many elastomeric materials and particularly natural rubber provide this kind of spring curve when subjected to uniaxial compression. In addition to providing variable rate spring curves, they also provide inherent vibration damping. Elastomeric springs typically take the form of solid blocks of elastomer or natural rubber.
When formed into hollow or cylindrical shapes and sealed with respect to external pressure, elastomeric springs may yield additional spring properties due to the compression of the air space within the hollow elastomeric body. For example, hollow elastomeric springs may provide spring properties generally similar to air springs while pressurized internally, or they may provide shock or load damping when selectively collapsible in response to the discharge of internal air pressure through a restricted orifice or the like. The spring effects thus obtained provide additional flexibility with respect to the variable rate spring curve obtained.
Hollow elastomeric springs, however, tend to be unstable, especially when formed with thin walls. To overcome this, some springs of this construction include a helical coil spring embedded within the wall of the elastomeric spring body. The composite elastomeric spring thus obtained is of generally tubular construction with opposed open ends. To pressurize this spring internally, it is necessary to establish continuous seals about both ends. Depending upon the construction of the load platens between which the spring is compressed, the seals tend to leak or break down both as the ends of the spring are deflected under load and as the spring resumes its relaxed state after compression.